There is growing evidence that alterations in gene expression contribute to the long-lasting effects of antipsychotic drugs on the brain. Project 4 contributes importantly to our understanding of the molecular actions of antipsychotic drugs by examining these phenomena at the chromatin level, and by thereby providing novel insight into the molecular basis of antipsychotic drug action. Project 4 will first characterize global changes in histone modifications induced by chronic antipsychotic drug exposure within striatal and prefrontal cortical regions of brain. Preliminary data, indicate that repeated haloperidol or clozapine administration increases levels of a repressive form of histone modification, methylation of Lys9 of histone H3, in these two regions. This effect is mediated via the upregulation of a particular Lys9-H3 methyltransferase, G9a. The proposed studies are aimed at characterizing the cell types within these regions where this drug-induced adaptation occurs and exploring its contribution to the behavioral actions of antipsychotic drugs in several rodent models. Using state-of-the-art chromatin methods, Project 4 will then identify the specific genes that show altered Lys9-H3 methylation, or alterations in other histone or DNA modifications, after chronic drug exposure. We also will study the role of two transcription factors, DeltaFosB and CREB, which are induced in striatal and prefrontal regions by antipsychotic drugs. This will include a cell type analysis of transcription factor regulation and altered binding to gene promoters genome-wide in response to drug exposure. By overlaying the results of these analyses with cell-type specific studies of mRNA expression in Projects 1 and 2, and biochemical studies in Project 3, we will identify antipsychotic drug targets with unique precision, and pursue a small number of targets for their functional role in antipsychotic drug action in our behavioral models. Finally, we will validate the regulation of histone modifications, transcription factors, and novel drug targets in postmortem tissue obtained from patients with schizophrenia. Together, these studies will advance our understanding of antipsychotic drug action, and provide novel approaches for the development of new drugs with improved efficacy and side effect profiles.